In the anime

Stunky stands on its two front legs and a purple ball appears at the end of its behind. Stunky then flips around and fires the purple ball at the opponent, causing a purple foul-smelling fog to appear and smell for twenty-four hours.

In the manga

In the Pokémon Adventures manga

Stunky turns around and releases a small seed from its behind towards the opponent. When the seed hits the ground, it releases a horrible smell all around the battlefield. The smell lasts for twenty-four hours.